Heating a home, cheaply?

Hello all, with the way natural gas prices are now we can't afford to run our central heating. We've put an electric heater in our bedroom, and pretty much stay in there when we're home now.

What are some ways you can think of to warm up a house, without paying for it? We let the heat in during the afternoon, but keep the house totally shut up mornings and evenings (including blinds). When I'm cooking, I'm intentionally not using the exhaust fan so that more heat stays inside.

I have cast iron pans that live in the oven, so if I need to preheat the oven for something, I'll let those pans get hot, and then place them around the dining room/kitchen area to warm the place up. I'll keep the kitchen/dining area closed off from the rest of the house, so this area stays warm for when we eat dinner.

If we have to use the dryer, then I'll strategically open doors so that the warmth from that spreads inwards to the house.

What other ways can you all think of to make the most of every scrap of warmth that we can get?